supplementary materials

Bis{2-[(2,4,6-trimethylphenyl)iminomethyl]pyrrol-1-ido}palladium(II)

The title compound, [Pd(C14H15N2)2], is a square-planar palladium complex composed of two deprotonated pyrrole-2-carbaldimine ligands coordinating a central PdII atom. In the crystal, three crystallographically independent complex molecules are observed, one of which is located in a general position, whereas the PdII atoms of the other molecules are situated on crystallographic inversion centers. The aromatic substituents at the imine N atoms in the three molecules show dihedral angles of 87.6 (7)/83.64 (7), 74.3 (7) and 88.3 (7)° with respect to the corresponding PdN4 plane.

In the course of a project related to the supramolecular structures of square
planar nickel and palladium complexes of pyrrole-2-carbaldehyde based Schiff
base ligands in comparison with the structures of the free ligands the
molecular structure of the title compound was determined. The free ligands
form centrosymmetric dimers via N—H···N hydrogen bonds between the
pyrrole NH function and the imine nitrogen atom of a neighboring molecule
(Crestani et al., 2011; Gomes et al., 2010;
Imhof, 2013).

In the crystal structure three crystallographically independent complexes are
observed of which one is located in a general position, whereas the palladium
atoms of the other molecules are situated on crystallographic inversion
centers (Figures 1–3). The aromatic substituents at the imine nitrogen atoms
show dihedral angles of 87.6 (7)° and 83.64 (7)° (molecule 1), 74.3 (7)°
(molecule 2) and 88.3 (7)° (molecule 3) with respect to the corresponding
PdN4 plane. As it is expected bond lengths in the NCCN backbone of the
ligands change upon coordination to palladium corresponding to a delocalized
formally anionic 1,4-diazadienyl subunit coordinating the metal atoms. Highly
related nickel and palladium complexes show similar structural features
(Anderson et al., 2006; Bellabarba et al., 2003;
Liang et
al., 2004; Pérez-Puente et al., 2008).

N-((1H-Pyrrol-2-yl)methylene)-2,4,6-trimethylaniline (213 mg, 1 mmol) and [Pd(PPh3)4] (580 mg, 0.5 mmol) were dissolved in 20 ml anhydrous
toluene under an argon atmosphere. After the solution is stirred at room
temperature for 2 h it was filtered through a short bed of celite. Afterwards
the solution was concentrated to ca 10 ml in vacuo. Crystalline
material of the title compound was obtained from this solution after 1 week at
-20°C (yield: 214 mg, 81%).

Hydrogen atoms have been included into the refinement in calculated positions
(methyl H atoms allowed to rotate but not to tip) with fixed thermal parameter
of Uiso(H) = 1.2 Ueq(C) for aromatic C—H groups and the
imine C—H function and a thermal parameter of Uiso(H) = 1.5
Ueq(C) for methyl groups.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.